Scalable implementation of quantum networks and photonic processors require integrated photonic memories with high efficiency, yet current integrated systems have been limited to storage efficiencies below 27.8%. Here, we demonstrate highly efficient integrated quantum memories based on rare-earth-iondoped crystals coupled with impedance-matched microcavities, realized in two novel architectures: 200-micrometer-thin membranes of Eu3+:Y2SiO5 integrated with fiber-based microcavities, and waveguide-based cavities fabricated using femtosecond lasers. Our approach achieves reliable integrated quantum storage with record efficiencies of 80.3(7)% for weak coherent pulses and 69.8(1.6)% for telecom-heralded single photons, alongside the storage of 20 temporal modes with an average efficiency of 51.3(2)%. Moreover, the thin-membrane Eu3+:Y2SiO5 architecture enables spectrally tunable efficient quantum storage via variable strain, providing a flexible interface for quantum networks. By combining high efficiency, large multimode capacity, and tunability, our devices establish a versatile hardware foundation for scalable quantum repeaters and chip-scale photonic processors.
Scalable implementation of quantum networks and photonic processors require integrated photonic memories with high efficiency, yet current integrated systems have been limited to storage efficiencies below 27.8%. Here, we demonstrate highly efficient integrated quantum memories based on rare-earth-iondoped crystals coupled with impedance-matched microcavities, realized in two novel architectures: 200-micrometer-thin membranes of Eu3+:Y2SiO5 integrated with fiber-based microcavities, and waveguide-based cavities fabricated using femtosecond lasers. Our approach achieves reliable integrated quantum storage with record efficiencies of 80.3(7)% for weak coherent pulses and 69.8(1.6)% for telecom-heralded single photons, alongside the storage of 20 temporal modes with an average efficiency of 51.3(2)%. Moreover, the thin-membrane Eu3+:Y2SiO5 architecture enables spectrally tunable efficient quantum storage via variable strain, providing a flexible interface for quantum networks. By combining high efficiency, large multimode capacity, and tunability, our devices establish a versatile hardware foundation for scalable quantum repeaters and chip-scale photonic processors.
We present a theoretical and device-oriented analysis of a hybrid quantum memory platformcombining integrated nanophotonic waveguides with rare-earth-ion-doped crystals operating at 4 K.The architecture bridges two regimes: (i) solid-state long-lived spin coherence in Eu3+ :Y2 SiO5 andPr3+ :Y2 SiO5 , and (ii) scalable photonic routing in SiN and TFLN integrated circuits.We derive performance bounds for evanescent coupling, multimode storage capacity, and end-to-end efficiency under experimentally realistic constraints. Our results indicate that such hybridsystems can operate as compact quantum repeater nodes with ∼ 102 –103 temporal modes, whilemaintaining ms-scale spin coherence and chip-scale footprint.Beyond theoretical modeling, we discuss implementation constraints and design trade-offs relevantto near-term nanophotonic fabrication platforms.
Advanced applications of quantum information science, such as long-distance quantum communication based on quantum repeaters, require photons to be interfaced with different devices. These devices, such as single photon detectors, quantum memories, quantum signal processors, and linear optical elements, may be integrated on a single chip to enable efficient, robust and scalable implementations. With aim of constructing a quantum repeater, and towards realizing integrated optical quantum memories and signal processors in general, we experimentally develop quantum light-matter interfaces using a cryogenically-cooled rare-earth-ion-doped waveguide, namely thulium-doped lithium niobate (Tm3+:LiNbO3). As the basis for our work, we describe a quantum repeater architecture that uses spectral multiplexing and quantum memories that operate with a fixed storage time. Our repeater architecture promises efficient operation, is compatible with the properties of cryogenically-cooled rare-earth-ion-doped crystals, and simplifies the demands of quantum memories compared to other architectures. To demonstrate the feasibility of our repeater design, we utilize our light-matter interface as a quantum memory to perform several experimental demonstrations. These include high-fidelity storage and retrieval of 26 spectrally-multiplexed quantum bits encoded into single-photon-level laser pulses, high-fidelity storage and retrieval of single and entangled photons derived from a photon-pair source, and high-visibility two-photon interference between weak laser pulses that are stored in one or two, separate, quantum memories. The unique properties of our light-matter interface allow us to demonstrate additional protocols that further highlight its promise for integrated quantum signal processing. By combining our Tm3+:LiNbO3 waveguide with a LiNbO3 waveguide phase modulator, we demonstrate operations such as sequencing, filtering, interference, and compression of laser pulses attenuated to the single-photon level. In another experiment, we measure the cross-phase modulation between strong pulses, by which we demonstrate photon-photon interactions that point towards non-destructive measurements of quantum bits. Since the performance of all aforementioned protocols, and future light-matter applications, hinge on the basic spectroscopic properties of our waveguide, we measure these properties at temperatures as low as 800 millikelvin. Our findings, discussed over several attached publications, usher the development of integrated quantum memories and processors for multi-component optical quantum information applications such as repeaters and networks.
Efficient and long-lived multimode quantum memories are crucial devices in the development of quantum technolgies. The reversible mapping of quantum states of light in rare earth doped crystals represents one of the most promising routes towards the realization of this goal. Such systems are also compatible with the miniaturization of quantum memories in integrated optics platforms, which offer unique features in terms of experimental scalability and enhanced light-matter interaction. Here, we fabricate single mode channel waveguides for 606 nm light in a praseodymium-doped yttrium orthosilicate crystal (Pr3+:Y2SiO5), that, thanks to its excellent coherence properties, is a widely studied material for light storage experiments. Waveguides are inscribed by femtosecond laser writing, adopting the so-called Type I configuration, where the core is directly obtained at the irradiated area. Remarkably, fabricating this kind of waveguides in crystals is a difficult task, as it requires to operate in a very narrow processing parameters window, if existing. We then use these waveguides for performing the storage and retrieval of single photons, implementing the atomic frequency comb protocol. We achieve a storage time of 5,5 µs, which is almost 2 orders of magnitude longer than previous realizations of quantum light storage in a waveguide. In addition, we investigate the potential information multiplexing capabilities of our system by performing the quantum storage of single photons delocalized over 14 different spectral modes. Our results show that laser written waveguides in rare earth-doped solid state systems are very promising for the development of efficient and long-lived multimode quantum memories.
The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extended storage times and large multimode capacities. Towards this goal, we experimentally demonstrate a memory platform operating at telecom wavelength using an Er3+:Y2SiO5 crystal. We record on-demand storage and recall of weak coherent pulses for up to 1 ms, exceeding by an order of magnitude that of previously reported demonstrations based on Er3+. The memory exhibits an efficiency of 10.36 % at 300 μs storage time with a signal-to-noise ratio of 10.9, mainly limited by spontaneous emission noise. We also store two spectral modes representing a frequency-bin encoding and retrieve the state with an overlap of 81.8 %. Furthermore, we demonstrate multimode capacity by simultaneously storing 20 temporal and 3 spectral modes with on-demand and selective recall capabilities, serving as a promising step toward a scalable quantum repeater architecture.
The faithful storage and coherent manipulation of quantum states with matter-systems would enable the realization of large-scale quantum networks based on quantum repeaters. To achieve useful communication rates, highly multimode quantum memories are required to construct a multiplexed quantum repeater. Here, we present a demonstration of on-demand storage of orbital-angular-momentum states with weak coherent pulses at the single-photon-level in a rare-earth-ion-doped crystal. Through the combination of this spatial degree-of-freedom (DOF) with temporal and spectral degrees of freedom, we create a multiple-DOF memory with high multimode capacity. This device can serve as a quantum mode converter with high fidelity, which is a fundamental requirement for the construction of a multiplexed quantum repeater. This device further enables essentially arbitrary spectral and temporal manipulations of spatial-qutrit-encoded photonic pulses in real time. Therefore, the developed quantum memory can serve as a building block for scalable photonic quantum information processing architectures.
Quantum memories for light are essential building blocks for quantum repeaters and quantum networks. Integrated operations of quantum memories could enable scalable application with low-power consumption. However, the photonic quantum storage lifetime in integrated devices has so far been limited to tens of microseconds, falling short of the requirements for practical applications. Here, we demonstrate quantum storage of photonic qubits for 1.021 milliseconds based on a laser-written optical waveguide fabricated in a 151 Eu 3+ :Y 2 SiO 5 crystal. Spin dephasing of 151 Eu 3+ is mitigated through dynamical decoupling applied via on-chip electric waveguides, and we obtain a storage efficiency of 12.0 ± 0.5% at 1.021 milliseconds, which is a demonstration of integrated quantum memories that outperforms the efficiency of a simple fiber delay line. Such long-lived waveguide-based quantum memory could support applications in quantum repeaters, and further combination with critical magnetic fields could enable potential application as transportable quantum memories.